Optical glass for precision molding, prefabricated glass, optical element and optical instrument

ABSTRACT

The invention provides a low-cost high-precision molding optical glass, with density below 4.54 g/cm 3 , refractive index ranging from 1.85 to 1.95, Abbe number ranging from 25 to 35 and transition temperature lower than 610° C. Expensive Ta 2 O 5  is not added in the invention, so the production cost is saved, and resource saving is realized; the combination of B 2 O 3  and La 2 O 3  effectively improves the devitrification resistance and the chemical stability of glass; the combination of WO 3  and TiO 2  allows the staining degree of the optical glass to be excellent; and the combination of Gd 2 O 3  and La 2 O 3  effectively improves the devitrification resistance of the glass.

TECHNICAL FIELD

The invention relates to an optical glass, in particular to ahigh-precision molding optical glass with refractive index ranging from1.85 to 1.95 and Abbe number ranging from 25 to 35, as well as to thepreform, optical element and optical apparatus made of said opticalglass.

BACKGROUND ART

In recent years, with the popularization of digital cameras andcamcorders, people demand more and more glass lens for major components.In addition, due to pixel increase of imaging device in the digitalcamera, optical elements like glass lens require higher performance.Since aspheric element could better eliminate the spherical aberrationand reduce the number of optical elements, aspheric element hits themainstream in optical design.

High-precision molding, a commonly used method for aspheric molding,refers to press molding of glass perform under high temperature by mouldfor female die with predetermined shape, in order to obtain the finalshape or glass molded article with shape similar to the final shape.Molded products with desired shape may be efficiently produced byhigh-precision molding. Besides, the aspheric lenses manufactured withhigh-precision molding technology usually no longer require grinding andpolishing, thereby reducing costs and improving productivity. In orderto replicate the high-precision modular surface on the glass moldingsduring high-precision molding, the glass preform is required to bepressurized under high temperature. At this point, shaping mould isexposed under high temperature with higher pressure. The surface layerof compression mold remains vulnerable to oxidative attack even underprotection. If expensive high-precision mould is frequently changedduring high-precision molding, low cost and high productivity will notbe achieved. To prolong the service life of mould and reduce damage tothe shaping mould by high-temperature environment, molding temperatureshall be reduced as much as possible. Therefore, optical materialdeveloper aims to develop optical glass with transition temperature (Tg)as low as possible.

Cost saving not only can realized by prolonging the service life ofshaping mould, but also by reducing raw material costs. CN1182058Cdiscloses a high-refractivity optical glass, in which a large amount ofhigh-cost Ta₂O₅ is applied, so it is not suitable for large-volumeindustrial production.

CONTENTS OF THE INVENTION

A technical problem to be solved by the invention is to provide alow-cost high-precision molding optical glass, with density (ρ) below4.54 g/cm³, refractive index (nd) ranging from 1.85 to 1.95, Abbe number(vd) ranging from 25 to 35 and transition temperature (Tg) lower than610° C.

To solve the technical problem, the invention provides thehigh-precision molding optical glass without Ta₂O₅, with density below4.54 g/cm³, refractive index ranging from 1.85 to 1.95, Abbe numberranging from 25 to 35 and transition temperature lower than 610° C.

Furthermore, components of the optical glass by weight percentage are asfollows: 2 to 10% of SiO₂, 12 to 22% of B₂O₃, 25 to 40% of La₂O₃, 1 to10% of ZrO₂, 5 to 12% of ZnO, 5 to 15% of TiO₂, 0 to 5% of GeO₂, 3 to15% of Gd₂O₃, 5 to 15% of Nb₂O₅, 1 to 8% of WO₃ and 0.1 to 1% of Li₂O.

Furthermore, SiO₂ accounts for 3 to 8%.

Furthermore, B₂O₃ accounts for 15 to 20% and La₂O₃ accounts for 30 to40%.

Furthermore, ZnO accounts for 5 to 10%.

Furthermore, TiO₂ accounts for 6 to 12% and WO₃ accounts for 1 to ₅%.

Furthermore, the content of TiO₂ is greater than 8% but less than orequal to 12%.

Furthermore, Gd₂O₃ accounts for 5 to 10% and La₂O₃ accounts for 30 to40%.

Furthermore, the content of Gd₂O₃ is greater than 5% but less than orequal to 10%.

Furthermore, the total content of Gd₂O₃ and La₂O₃ is 36 to 45%.

Furthermore, ZrO₂ accounts for 3 to 8%, GeO₂ accounts for 0 to 2%, Nb₂O₅accounts for 8 to 14% and Li₂O accounts for 0.5 to 1%.

Furthermore, the total content of SiO₂, B₂O₃, La₂O₃, ZrO₂, ZnO, TiO₂,Gd₂O₃, Nb₂O₅, WO₃ and Li₂O is greater than 95%.

Furthermore, the total content of SiO₂, B₂O₃, La₂O₃, ZrO₂, ZnO, TiO₂,Gd₂O₃, Nb₂O₅ and Li₂O is greater than 93%.

The components of high-precision molding optical glass by weightpercentage are as follows: 2 to 10% of SiO₂, 12 to 22% of B₂O₃, 25 to40% of La₂O₃, 1 to 10% of ZrO₂, 5 to 12% of ZnO, 5 to 15% of TiO₂, 0 to5% of GeO₂, 3 to 15% of Gd₂O₃, 5 to 15% of Nb₂O₅, 1 to 8% of WO₃ and 0.1to 1% of Li₂O.

Furthermore, SiO₂ accounts for 3 to 8%. Furthermore, B₂O₃ accounts for15 to 20% and La₂O₃ accounts for 30 to 40%. Furthermore, ZrO₂ accountsfor 3 to 8%.

Furthermore, ZnO accounts for 5 to 10%. Furthermore, TiO₂ accounts for 6to 12% and WO₃ accounts for 1 to 5%.

Furthermore, the content of TiO₂ is greater than 8% but less than orequal to 12%.

Furthermore, GeO₂ accounts for 0 to 2%.

Furthermore, Gd₂O₃ accounts for 5 to 10% and La₂O₃ accounts for 30 to40%.

Furthermore, the content of Gd₂O₃ is greater than 5% but less than orequal to 10%.

Furthermore, the total content of Gd₂O₃ and La₂O₃ is 36 to 45%.

Furthermore, Nb₂O₅ accounts for 8 to 14%.

Furthermore, Li₂O accounts for 0.5 to 1%.

Furthermore, the total content of SiO₂, B₂O₃, La₂O₃, ZrO₂, ZnO, TiO₂,Gd₂O₃, Nb₂O₅, WO₃ and Li₂O is greater than 95%.

Furthermore, the total content of SiO₂, B₂O₃, La₂O₃, ZrO₂, ZnO, TiO₂,Gd₂O₃, Nb₂O₅ and Li₂O is greater than 93%.

A glass preform made of the above-mentioned high-precision moldingoptical glass.

An optical element made of the above-mentioned high-precision moldingoptical glass.

An optical apparatus made of the above-mentioned high-precision moldingoptical glass.

The optical glass provided by the invention is advantageous in thatexpensive Ta₂O₅ is not added, which reduces production costs and savesresources; the devitrification resistance of glass may be effectivelyimproved and chemical stability be strengthened through the combinationof B₂O₃ and La₂O₃; excellent staining degree is achieved by thecombination of WO₃ and TiO₂; the devitrification resistance of glass maybe effectively improved by the combination of Gd₂O₃ and La₂O₃ as well,and a high-precision molding optical glass with refractive index rangingfrom 1.85 to 1.95, Abbe number ranging from 25 to 35, glass transitiontemperature lower than 610° C. and density below 4.54 g/cm³ can beobtained.

DESCRIPTION OF EMBODIMENTS

Each component of the optical glass provided by the invention isdescribed hereunder, and the content thereof is represented by wt %unless otherwise stated.

SiO₂ is an oxide forming glass network, and adding a certain amount ofSiO₂ can increase the high temperature viscosity and improve thedevitrification resistance of glass. When the content of SiO₂ is lowerthan 2%, the effects are not obvious; while when the content exceeds10%, the melting behavior of glass is liable to be poor and it is hardto remove the bubbles. Therefore, the content of SiO₂ is 2 to 10%,preferably 3 to 8%.

B₂O₃ is also an oxide forming glass network, and an essential componentto improve the melting behavior to reduce the viscosity of glass. It canbe used as solvent in the glass melting process. When the content ofB₂O₃ is less than 12%, it is difficult to obtain stable glass and thedevitrification resistance is unsatisfactory; but when the content ofB₂O₃ is higher than 22%, the refractive index of glass cannot reach thedesign goal and the chemical stability of glass will be reduced.Therefore, the content of B₂O₃is 12 to 22%, preferably 15 to 20%.

La₂O₃, as a main component of high-refractivity optical glass, canincrease the refractive index of glass and not obviously increase thedispersion of glass. In the formulation provided in the invention, thecombination of B₂O₃ and La₂O₃ may effectively improve thedevitrification resistance and strengthen the chemical stability ofglass. However, when the content of La₂O₃ is less than 25%, such effectcannot be achieved; while when the content exceeds 40%, thedevitrification resistance of glass is liable to be poor. Therefore, thecontent of La₂O₃ is 25 to 40%, preferably 30 to 40%.

ZrO₂ can improve the viscosity, hardness and chemical stability of glassand lower the coefficient of thermal expansion of glass. When thecontent of ZrO₂ exceeds 10%, the glass is liable to be refractory andprone to devitrification, and the chemical stability of glass becomespoor. Therefore, the content of ZrO₂ is preferably 1 to 10%, morepreferably 3 to 8%.

ZnO, as an essential component of high-precision molding optical glassprovided by the invention, could help lower the melting temperature andtransition temperature of glass, and adjust the optical properties ofglass. When the content of ZnO is less than 5%, the transitiontemperature of glass will increase; while when the content is higherthan 12%, devitrification tends to increase and high-temperatureviscosity of the glass decreases, bringing great difficulties in glassmolding. Therefore, the content of ZnO is preferably 5 to 12%, morepreferably 5 to 10%.

WO₃ can adjust the optical constant and devitrification resistance ofglass. Especially in lanthanide optical glass, WO₃ can effectivelyimprove the devitrification resistance of glass and transmittance willnot be damaged too much. Experiments show that when the content of WO₃exceeds 8%, the devitrification resistance of glass is liable to bedegraded, so the content of WO₃ is preferably 1 to 8%, more preferably 1to 5%.

TiO₂ enables the glass to enjoy high refractivity, but over-high contentwill greatly reduce the dispersion coefficient and devitrification tendsto increase, or even significantly increase the staining degree. Throughresearches, the inventor found that excellent staining degree isachieved by the combination of WO₃ and TiO₂ in the present invention.Therefore, the content of TiO₂ is preferably 5 to 15%, more preferably 6to 12%, and most preferably greater than 8% but less than or equal to12%.

GeO₂ can enhance the refractive index and thermal stability of glass,but if the content thereof is greater than 5%, the thermal stability ofglass is liable to be degraded. Thus, the content of GeO₂ is preferably0 to 5%, more preferably 0 to 2%.

Gd₂O₃ can increase the refractive index and thermal stability of glass.If certain amount of Gd₂O₃ is molten together with La₂O₃, thedevitrification resistance of glass may be effectively improved. Whenthe content of Gd₂O₃ is less than 3%, the effects are not obvious; whilewhen the content of Gd₂O₃ exceeds 15%, the devitrification resistance ofglass is liable to be poor. Therefore, the content of Gd₂O₃ is 3 to 15%,more preferably 5 to 10%, most preferably greater than 5% but less thanor equal to 10%.

When the total content of Gd₂O₃ and La₂O₃ is 36 to 45%, thedevitrification resistance of glass may be more effectively improved,thus realizing the optical performance required by the invention.

Nb₂O₅ can increase the refractive index and improve the chemicaldurability and devitrification resistance. When the content of Nb₂O₅ isless than 5%, the effects are not obvious; while when the content ofNb₂O₅ exceeds 15%, the devitrification resistance is liable to be poorand the softening temperature of glass goes up, so the content of Nb₂O₅is preferably 5 to 15%, more preferably 8 to 14%.

Li₂O can significantly reduce the transition temperature of glass andeffectively improve the melting behavior of glass, but when its contentexceeds 1%, the devitrification resistance and chemical stability ofglass is liable to be poor. Therefore, the content of Li₂O is 0.1 to 1%,preferably 0.5 to 1%.

On the premise of ensuring the optical glass provided by the inventionenjoy the refractive index ranging from 1.85 to 1.95 and Abbe numberranging from 25 to 35, in order to more effectively improve thedevitrification resistance and chemical stability of glass, the totalcontent of SiO₂, B₂O₃, La₂O₃, ZrO₂, ZnO, TiO₂, Gd₂O₃, Nb₂O₅, WO₃ andLi₂O applied in the present invention is greater than 95%, morepreferably, the total content of SiO₂, B₂O₃, La₂O₃, ZrO₂, ZnO, TiO₂,Gd₂O₃, Nb₂O₅ and Li₂O is greater than 93%.

In the following paragraphs, the performance of high-precision moldingoptical glass provided in the present invention will be described:

Refractive index (nd) refers to annealing value from −2° C./h to −6°C./h. The refractive index and Abbe number are measured as per the TestMethods of Colorless Optical Glass—Refractive Index and Coefficient ofDispersion (GB/T 7962.1-1987).

Transition temperature (Tg) is tested as per Test Methods of ColorlessOptical Glass—Linear Thermal Expansion Coefficient, TransitionTemperature and Yield Point Temperature (GB/T 7962.16-1987), namely,placing the tested sample in a certain temperature range, extendingstraight lines of a low-temperature region and a high-temperature regionon an expansion curve of the tested sample for each 1 degree centigraderise in temperature, intersecting the straight lines, wherein thetemperature corresponding to the intersection point is the Tg.

The density is tested as per Colorless Optical Glass TestMethods—Density (GB/T 7962.20-1987).

The glass is processed into a sample which is 10 mm plus or minus 0.1 mmthick, and then the wavelength λ₇₀ corresponding to the transmissivityof 70% is tested.

The test shows that the optical glass provided by the invention has thefollowing properties that the density is below 4.54 g/cm³, refractiveindex (nd) ranges from 1.85 to 1.95, Abbe number (vd) ranges from 25 to35, transition temperature (Tg) is lower than 610° C. and the wavelengthλ₇₀ corresponding to the transmissivity of 70% is less than 430 nm.

The invention also provides an optical element made of said opticalglass with the method that is well known by technical personnel in theart. Since the optical glass enjoys high refractive index and low glassTg, the optical element also enjoys high refractive index and low glassTg and is applicable to digital cameras, digital video cameras andcamera phones, etc.

To further understand the technical scheme of the present invention,embodiments of optical glass provided in the invention are described asbelow. What shall be noted is that these embodiments do not limit thescope of this invention.

The optical glasses (embodiments 1˜30) shown in Tables 1 to 3 are formedby weighting based on the proportions of each embodiment in Tables 1 to3, mixing the ordinary raw materials for optical glass (such as oxide,hydroxide, carbonate and nitrate), placing the mixed raw materials in aplatinum crucible, melting under the temperature of 1100 to 1300° C.,obtaining homogeneous molten glass without bubbles and undissolvedsubstances after melting, clarification, stirring and homogenization,shaping the molten glass in a mould and perform annealing.

Tables 1 to 3 show the composition of embodiments 1˜30 of the inventionand refractive index (nd), Abbe number (vd), density (ρ), glasstransition temperature (Tg) and wavelength λ₇₀ corresponding to thetransmissivity of 70%. The composition of each component is representedby wt % in such tables.

TABLE 1 Embodiments Composition 1 2 3 4 5 6 7 8 9 10 SiO₂ 2.05 9.87 3.035.89 5.21 4.85 5.33 6.18 7.34 3.52 B₂O₃ 21.84 12.12 19.88 15.1 16.2118.68 16.44 18.22 17.24 16.1 La₂O₃ 25.03 35.39 30.05 39.78 28.02 38.5835.2 34.32 32.33 37.15 ZrO₂ 9.90 1.11 7.76 3.04 4.36 4.56 6.57 5.24 4.556.22 ZnO 8.20 11.87 5.03 5.64 9.85 6.32 7.64 8.22 6.39 6.38 TiO₂ 5.0314.92 8.88 8.04 11.89 7.65 8.34 7.65 6.35 10.25 GeO₂ 0 4.86 1.89 0.680.89 1.05 1.52 0.86 1.25 0.52 Gd₂O₃ 14.91 3.01 9.96 5.01 8.32 6.13 6.687.65 8.47 6.35 Nb₂O₅ 5.1 4.86 8.12 13.92 10.2 9.22 8.46 8.69 12.68 9.14WO₃ 6.94 1.04 4.89 2.3 4.31 2.14 3.11 2.34 2.57 3.65 Li₂O 1.00 0.95 0.510.6 0.74 0.82 0.71 0.63 0.83 0.72 nd 1.86 1.87 1.90 1.95 1.86 1.93 1.921.89 1.88 1.91 vd 35.0 30.5 30.2 27.6 32.6 29.4 30.5 29.5 33.7 29.6 Tg(° C.) 597 586 609 602 601 592 593 596 602 604 ρ (g/cm³) 4.23 4.46 4.484.53 4.31 4.52 4.50 4.35 4.47 4.48 λ₇₀ (nm) 388 409 417 428 407 420 417408 395 417

TABLE 2 Embodiments Composition 11 12 13 14 15 16 17 18 19 20 SiO₂ 3.917.3 5.68 6.3 6.62 5.1 4.84 7.21 4.5 6.2 B₂O₃ 20.34 16.1 15.3 17.2 17.414.2 18.2 17.68 14.28 15.3 La₂O₃ 26.43 28.3 33.83 35.03 29.47 36.69 33.232.81 37.2 34.6 ZrO₂ 8.08 9.3 7.92 5.11 6.45 5.4 8.11 7.33 5.74 6.04 ZnO7.44 10 6.14 6.18 8.68 7.5 7.35 8.16 7.33 6.45 TiO₂ 5.63 9.4 10.1 7.339.2 8.1 7.36 8.63 7.39 11.2 GeO₂ 0.58 3.24 0.63 1.2 0.91 1.3 0.99 0.820.94 0.84 Gd₂O₃ 13.1 4.21 8.39 6.58 7.33 6.44 7.34 6.43 7.36 6.15 Nb₂O₅6.3 8.95 7.46 11.24 9.1 10.1 7.56 6.85 10.5 9.07 WO₃ 7.64 2.68 3.88 3.254.3 4.5 4.33 3.24 4.02 3.52 Li₂O 0.55 0.52 0.67 0.58 0.54 0.67 0.72 0.840.74 0.63 nd 1.89 1.88 1.91 1.91 1.90 1.94 1.91 1.88 1.93 1.92 vd 33.830.1 29.2 30.4 30.9 29.8 32.5 30.4 29.8 29.6 Tg (° C.) 608 597 601 603599 602 600 589 592 602 ρ (g/cm³) 4.42 4.40 4.47 4.49 4.48 4.54 4.504.42 4.51 4.50 λ₇₀ (nm) 398 407 419 422 419 427 412 405 424 421

TABLE 3 Embodiments Composition 21 22 23 24 25 26 27 28 29 30 SiO₂ 5.35.1 5.22 5.89 4.61 4.45 5.14 4.85 4.06 4.8 B₂O₃ 17.6 16.8 17 16.9 17.217.36 16.78 17.1 16.85 17.2 La₂O₃ 33.41 34.98 34.15 34.46 35.21 34.234.51 35.45 34.16 34.31 ZrO₂ 5.34 5.3 4.96 5.1 5.2 5.01 5.33 4.68 5.115.01 ZnO 7.64 7.2 6.58 6.87 7.11 7.33 6.84 7.38 7.61 7.38 TiO₂ 8.33 8.319.1 8.34 9.14 8.69 9.15 8.42 8.78 8.56 GeO₂ 1.01 0.96 0.86 1.2 0.89 1.020.91 1.36 1.05 0.82 Gd₂O₃ 7.3 7.01 6.85 6.12 6.69 7.82 7.33 6.85 7.468.1 Nb₂O₅ 10.3 10.67 11.4 11.52 10.12 10.5 10.45 10.58 11.1 10.65 WO₃3.12 2.96 3.2 2.94 3.1 2.96 2.84 2.64 3.15 2.38 Li₂O 0.65 0.71 0.68 0.660.73 0.66 0.72 0.69 0.67 0.79 nd 1.91 1.92 1.90 1.89 1.90 1.91 1.90 1.911.92 1.90 vd 29.8 29.9 30.3 31.2 30.6 30.9 30.6 31.1 30.4 30.3 Tg (° C.)601 593 602 598 596 604 595 603 602 590 ρ (g/cm³) 4.53 4.52 4.51 4.484.51 4.51 4.49 4.50 4.52 4.50 λ₇₀ (nm) 419 425 416 407 418 418 419 417426 417

As illustrated in the above embodiments, the optical glass provided bythe invention is characterized by density (ρ) below 4.54 g/cm³,refractive index (nd) ranging from 1.85 to 1.95, Abbe number (vd)ranging from 25 to 35, transition temperature (Tg) lower than 610° C.and wavelength λ₇₀ corresponding to the transmissivity of 70% below 430nm, and is applicable to high-precision molding.

1. A high-precision molding optical glass, not comprising Ta₂O₅, withdensity below 4.54 g/cm3, refractive index ranging from 1.85 to 1.95,Abbe number ranging from 25 to 35 and transition temperature lower than610° C.
 2. The high-precision molding optical glass according to claim1, comprising by weight percentage as follows: 2 to 10% of SiO₂, 12 to22% of B₂O₃, 25 to 40% of La₂O₃, 1 to 10% of ZrO₂, 5 to 12% of ZnO, 5 to15% of TiO₂, 0 to 5% of GeO₂, 3 to 15% of Gd₂O₃, 5 to 15% of Nb₂O₅, 1 to8% of WO₃ and 0.1 to 1% of Li₂O.
 3. The high-precision molding opticalglass according to claim 2, wherein SiO₂ accounts for 3 to 8%.
 4. Thehigh-precision molding optical glass according to claim 2, wherein B₂O₃accounts for 15 to 20% and La₂O₃ accounts for 30 to 40%.
 5. Thehigh-precision molding optical glass according to claim 2, wherein ZnOaccounts for 5 to 10%.
 6. The high-precision molding optical glassaccording to claim 2, wherein TiO₂ accounts for 6 to 12% and WO₃accounts for 1 to 5%.
 7. The high-precision molding optical glassaccording to claim 2, wherein the content of TiO₂ is greater than 8% butless than or equal to 12%.
 8. The high-precision molding optical glassaccording to claim 2, wherein Gd₂O₃ accounts for 5 to 10% and La₂O₃accounts for 30 to 40%.
 9. The high-precision molding optical glassaccording to claim 2, wherein the content of Gd₂O₃ is greater than 5%but less than or equal to 10%.
 10. The high-precision molding opticalglass according to claim 2, wherein the total content of Gd₂O₃ and La₂O₃is 36 to 45%.
 11. The high-precision molding optical glass according toclaim 2, wherein ZrO₂ accounts for 3 to 8%, GeO₂ accounts for 0 to 2%,Nb₂O₅ accounts for 8 to 14% and Li₂O accounts for 0.5 to 1%.
 12. Thehigh-precision molding optical glass according to claim 2, wherein thetotal content of SiO₂, B₂O₃, La₂O₃, ZrO₂, ZnO, TiO₂, Gd₂O₃, Nb₂O₅, WO₃and Li₂O is greater than 95%.
 13. The high-precision molding opticalglass according to claim 2, wherein the total content of SiO₂, B₂O₃,La₂O₃, ZrO₂, ZnO, TiO₂, Gd₂O₃, Nb₂O₅ and Li₂O is greater than 93%.
 14. Ahigh-precision molding optical glass, comprising by weight percentage asfollows: 2 to 10% of SiO₂, 12 to 22% of B₂O₃, 25 to 40% of La₂O₃, 1 to10% of ZrO₂, 5 to 12% of ZnO, 5 to 15% of TiO₂, 0 to 5% of GeO₂, 3 to15% of Gd₂O₃, 5 to 15% of Nb₂O₅, 1 to 8% of WO₃ and 0.1 to 1% of Li₂O.15. The high-precision molding optical glass according to claim 14,wherein SiO₂ accounts for 3 to 8%.
 16. The high-precision moldingoptical glass according to claim 14, wherein B₂O₃ accounts for 15 to 20%and La₂O₃ accounts for 30 to 40%.
 17. The high-precision molding opticalglass according to claim 14, wherein ZrO₂ accounts for 3 to 8%.
 18. Thehigh-precision molding optical glass according to claim 14, wherein ZnOaccounts for 5 to 10%.
 19. The high-precision molding optical glassaccording to claim 14, wherein TiO₂ accounts for 6 to 12% and WO₃accounts for 1 to 5%.
 20. The high-precision molding optical glassaccording to claim 14, wherein the content of TiO₂ is greater than 8%but less than or equal to 12%.
 21. The high-precision molding opticalglass according to claim 14, wherein GeO₂ accounts for 0 to 2%.
 22. Thehigh-precision molding optical glass according to claim 14, whereinGd₂O₃ accounts for 5 to 10% and La₂O₃ accounts for 30 to 40%.
 23. Thehigh-precision molding optical glass according to claim 14, wherein thecontent of Gd₂O₃ is greater than 5% but less than or equal to 10%. 24.The high-precision molding optical glass according to claim 14, whereinthe total content of Gd₂O₃ and La₂O₃ is 36 to 45%.
 25. Thehigh-precision molding optical glass according to claim 14, whereinNb₂O₅ accounts for 8 to 14%.
 26. The high-precision molding opticalglass according to claim 14, wherein Li₂O accounts for 0.5 to 1%. 27.The high-precision molding optical glass according to claim 14, whereinthe total content of SiO₂, B₂O₃, La₂O₃, ZrO₂, ZnO, TiO₂, Gd₂O₃, Nb₂O₅,WO₃ and Li₂O is greater than 95%.
 28. The high-precision molding opticalglass according to claim 14, wherein the total content of SiO₂, B₂O₃,La₂O₃, ZrO₂, ZnO, TiO₂, Gd₂O₃, Nb₂O₅ and Li₂O is greater than 93%.
 29. Aglass preform made of said high-precision molding optical glassaccording to claim
 1. 30. An optical element made of said high-precisionmolding optical glass according to claim
 1. 31. An optical apparatusmade of said high-precision molding optical glass according to claim 1.